Preparation and manipulation of high quality cells or biomolecules are primary requirements for a variety of diagnostic or therapeutic applications. Though filtration techniques are commonly used for capturing cells, they pose various challenges including the inability to obtain high separation efficiencies for heterogeneous cell populations, clogging of pores or harsh filtration conditions causing cellular damage. The challenges are exacerbated when filtering larger volumes of crude biological samples. In addition to filtration, a number of microfluidic separation techniques exist that rely on the application of a force, which acts to push or pull cells in a direction perpendicular to the direction of flow of the sample fluid being processed. Several of these continuous flow techniques may be useful in efficiently separating out cells from blood, including hydrodynamic filtration, inertial and deterministic lateral flow separation. However, in other embodiments the method may require pre-dilution of the blood sample and are limited to relatively low volumetric flow rates.
Recent developments on “filter-free” mechanisms for biological sample preparation offer portable purification devices for limited volumes. Primary applications have been in point-of-care diagnostics, where relatively small samples are collected and directly processed within the collection vessel. However, there remains a need to expand these simple separation methods to larger volumetric flow rates to provide alternatives to large scale centrifugation and filtration techniques.
A continuous flow separation technique is field flow fractionation (FFF) in which differential retention of particulates being eluted through a microchannel results in separation of particulates having different characteristics. However, the relevance of FFF for whole blood separation remains uncertain as FFF often requires relatively dilute starting blood samples. While combinations of separation techniques, such as hydrodynamic filtration and inertial focusing, have increased throughput limits associated with continuous flow separations. These “high throughput” implementations require carefully controlled flow rates and/or upstream sample pre-filtration or dilution.
Sedimentation-based devices may provide simpler methods of cell and/or particulate separation from fluids containing them without the need for careful fluid flow control and/or excessive sample dilution. However, there exists a need to provide devices and methods that enable high-speed separation of particulates such as cells and/or dispersed particulates from fluids containing them without the need to augment sedimentation rates via capital intensive equipment, such as centrifuges. A fast and efficient separation and collection of particulates or cells from a large sample volume without complex equipment is an unmet need. Therefore, inexpensive devices that can accelerate particulate separation via sedimentation, and enable use of a large sample volume with minimal human intervention are highly desirable.